1. Field of the Invention
This invention relates to a maleimide resin composition suitably allowing encapsulation of a semiconductor element and to a resin encapsulated semiconductor device manufactured using the composition.
2. Description of the Related Art
Recently, rapid increase is progressing in fining various function units of a semiconductor element and in size of the element. An epoxy resin composition containing a thermosetting epoxy resin as a resin component and a phenolic resin as a curing agent is widely used for resin encapulation of the semiconductor element.
A flat package-type IC, for example, a gate array called ASIC (Application specific IC) and a standard cell-type LSI, encapuslated with the resin composition described above is mounted on a substrate by processes of vapor phase re-flow, infrared re-flow, and soaking in solder. In these process, the package is exposed to high temperature (ca. 215.degree.-260.degree. C.). Then, in the resin encapsulated semiconductor encapsulated with said epoxy resin composition, very small amount of water permeated through resin to inside abruptly evaporates allowing to crack the encapsulating resin. Crack developed to outside spoils moisture-resistance reliability of the resin encapsulated semiconductor to make a great problem. Besides, a phenomenon occurs to disturb to mount the package due to swelling of the encapsulated resin.
Inside the semiconductor element encapsulated with the resin composition in the processes described above, the following problems frequently occurs: crack occurred in PSG (phoshor silicate glass) and SiN (silicon nitride) used as a passivation film formed on a wiring layer of aluminum; cutting of Au bonding wires.
For measures for these problems, the following requirements have increased intensively for the encapsulating resin used for manufacturing a large package.
1) To decrease stress against an object encapsulated with the encapsulating resin and to increase adhesion of encapsulating resin to PSG, SiN, polyimde film, and lead frame. PA1 2) To give high-temperature strength corresponding to mounting temperature and high-temperature strength with moisture absorbance to the encapsulating resin and to reduce moisture absorbance.
On the basis of the above views, utilizing for main resin components of the encapsulating resin composition is being evaluated for such as maleimide resins, PPS (polyphenylene sulfide) resin, PPO (polyphenylene oxide) resin, and a liquid crystal polymer. Recent candidates of the encapsulating resin proposed are combined resins of maleimide and epoxy resins or amino-bis-maleimide resin made by combining bis-maleimide resin and 4,4'-diaminodiphenylmethane. Generally, encapsulation of a semiconductor element using these maleimide resins is made by molding a resin composition containing a maleimide resin as a main component of resin, a phenolic resin as a curing agent component, a curing catalyst, and other additives such as an inorganic filler and a flame-retardant, employing normal molding process, such as transfer molding. It is said that the additional reaction of the phenolic resin to double bonds of the maleimide resin contained in the resin composition and the mutual reaction of maleimide resins occur in the molding process to cure the composition by polymerization of the maleimide resin resulting in the yield of the encapusulating resin moldings.
The following problems occur at resin encapsulation of a semiconductor element using the maleimide resin composition described above. In comparison with the epoxy resin composition containing a phenolic resin as a curing agent, the maleimide resin composition shows less curing characteristics, because the reaction between the maleimide resin and the phenolic resin slowly progresses in said maleimide resin composition. Hence, molding resin for encapsulating requires long time to result in remaining non-reacted components and in decrease in mold release characteristics from a mold used.
In addition, monomer and low molecular substance remain in the resin composition to make stain on the mold. The encapsulating resin moldings results in problems such as inferior appearance.
Consequently, though use of the maleimide resin composition for resin encapsulation of a semiconductor element solves problems in the use of the conventional epoxy resin composition, the use causes a problem of very inferior properties such as moldability.